Valve, Especially Proportional Pressure Control Valve

ABSTRACT

The invention relates to a valve, especially a proportional pressure control valve, comprising a valve housing ( 38 ) provided with at least three fluid connections ( 1, 2, 3 ). The valve can be connected to a hydraulic drive system with a pre-determinable minable consumer pressure. The aim of the invention is to create a valve that can perform reliable valve switching functions even for low-viscous fluid media, and to reduce the susceptibility to disturbance variables. To this end, a valve piston ( 56 ), which is actively connected to a pilot seat ( 58 ) by means of an energy accumulator ( 62 ), can be controlled by means of a control device ( 40 ), and the consumer pressure on a fluid connection ( 1 ) acts at least on the valve piston ( 56 ) in such a way that, according to the consumer pressure and the actuating force of the control device ( 40 ), a fluid can flow between the two other fluid connections ( 2  and  3 ) in both directions inside the valve housing ( 38 ).

The invention relates to a valve, especially a proportional pressure control valve, with a valve housing with at least three fluid ports, the valve being connectable to a hydraulic drive system with a definable consumer pressure.

Proportional pressure control valves (U.S. Pat. No. 4,316,599) are known which among other things form control valves for oil hydraulic systems which deliver an essentially constant output pressure for a variable input pressure. The output pressure to be controlled is dictated by the current signal which is delivered by the corresponding trigger electronics and which acts on the actuating magnet as the magnet system. The actuating magnet can be made as a pressure-tight oil bath magnet and has a long service life.

Proportional pressure control valves such as these can be directly controlled piston sliding valves in a three-way design, i.e., with output side pressure safeguarding. They are used among other things in oil hydraulic systems to control clutches in shift transmissions for controlled influencing of pressure build-up and pressure drop, for remote pressure setting, and also for controlling pressure variations and for pilot control of hydraulic valves and logic elements.

These conventional proportional pressure control valves have poor stability especially for thin-liquid fluid media, i.e., they begin to “oscillate”; this is especially harmful when the known valves are designed to perform special functions, for example in motor vehicle power steering systems, hydraulic drive units, and other safety engineering-relevant domains. It has generally been found that when pressure control valves are used, susceptibility to fault variables lies in the natural frequency region of the valve, and the instabilities which occur can lead to failure of the valve and the pertinent parts of a hydraulic system.

In the prior art, multiaxle drive units for elevating work platforms are known which generally have a rear drive and optional all-wheel drive. To ensure safe operation with driving of only one axle and a free-running of the other axle and execution of braking processes with sudden stopping, in the known solution a plurality of valve components is necessary, such as two so-called shock valves, two counter balance valve combinations, consisting of one pressure control valve and one 2/2-way valve each, and a 2/2-way valve as the recirculation valve. This functional structure is reliable in operation, but due to the plurality of valves its failure in operation must be expected; this shortens maintenance intervals. The known solution also requires a large amount of installation space and is expensive to manufacture due to the diversity of parts.

On the basis of this prior art, the object of the invention is to devise a valve, especially a proportional pressure control valve, which has good stability when thin-liquid fluid media are used, and which especially when used in safety-relevant domains including hydraulic drive unit helps reduce the diversity of components. This object is achieved by a valve with the features of claim 1 in its entirety.

In that, as specified in the characterizing part of claim 1, it is possible for a control means to trigger a valve piston which is dynamically connected to a pilot seat by means of an energy storage device and because the prevailing consumer pressure at one fluid port acts at least on the valve piston such that depending on the prevailing consumer pressure and on the actuating force of the control means, fluid can flow between the two other fluid ports in both directions within the valve housing, a valve is devised which even for thin-liquid fluid media can perform reliable valve operating functions and susceptibility to fault quantities is reduced. If the valve is used within completely hydraulic systems, such as hydraulic drive units, the shock valves, counter balance valves and directional control valves used in the past can be replaced by a base valve, and essentially the same switching and operating functions can then be implemented with only one valve according to the invention. This reduces the production and maintenance costs, and since within the drive unit only one valve need be managed, operating reliability overall is increased.

Other advantageous embodiments of the valve according to the invention are the subject matter of the other dependent claims.

The valve according to the invention, especially a proportional pressure control valve, will be detailed below using various embodiments. The figures are schematic and not to scale.

FIG. 1 shows, in the form of a hydraulic circuit diagram, parts of a hydraulic elevating work platform according to the prior art;

FIG. 2 shows the circuit representation according to FIG. 1, but referenced to the solution according to the invention;

FIGS. 3 to 5 show in a lengthwise section different embodiments of the valve according to the invention, in FIG. 3 the shuttle valve as shown in FIG. 2 being included for the purposes of more detailed explanation.

FIG. 1 shows in the form of a circuit diagram parts of a hydraulic drive unit for a scissors lift platform which is not detailed. These vehicles generally have two axles, and generally a rear drive is implemented and the front axle can be separately actuated for implementation of optional all-wheel drive, the drives for the two axles being designed to be essentially the same. FIG. 1 for the prior art shows a hydraulic motor 10 as the driving means for the axle of the pertinent vehicle, which axle is not detailed; depending on the operating position of the 4/3-way valve 12 in both directions of rotation the motor can be driven in both directions of rotation for forward or backward operation and for implementing a braking function. The 4/3-way valve 12 according to FIG. 1 is shown in the neutral position and otherwise is connected on the input side to the hydraulic pump 14 and to a tank 16.

The supply line of the hydraulic pump 14 is safeguarded via a conventional pressure control valve 18. Two parallel running supply lines 20 run to the respective input sides of the hydraulic motor 10 and between the two supply lines 20 in a parallel connection there are different valves such as a recirculation valve 22, two counter balance valves 24 to which one pressure control valve 26 at a time is assigned, and two other pressure control valves 28 as so-called shock valves. In the region of the connection sites of the shock valve 28 which is located topmost viewed in the direction of looking at FIG. 1, two secondary lines 30 are connected oppositely to the two supply lines and lead back to the tank which is safeguarded by way of check valves. These check valves are used as replenishing valves to prevent cavitation. Altogether the known solution therefore has two shock valves 28, two counter balance valves 24 with pressure control valves 26 and one recirculation valve 22, the two counter balance valves 24 and the recirculation valve 22 being made in the form of 2/2-way valves.

In order to explain operation of the known drive unit as shown in FIG. 1 in greater detail, a typical operating sequence is reproduced below. If for example when only one axle (rear drive) is driven, the second axle is entrained in free running, the recirculation valve 22 is switched into its enabling position shown in FIG. 1 so that the oil returning from the hydraulic or traveling motor 10 is routed back to the motor in order to avoid running dry. In traveling operation with only one drive axle, the 4/3-way valve 12 remains off, so that all the pump oil is routed to the active axle and thus the speed is doubled.

If a braking process is to be carried out, the pertinent inactive axle can be engaged to support the braking process. To this end, the recirculation valve 22 is blocked, and depending on the braking direction, the other 2/2-valve 24 is switched as a counter balance valve which in this way clears the fluid-carrying path via an additional pressure control valve 26 which is assigned to it. Since for this braking possibility in two opposite traveling directions the arrangement as shown in FIG. 1 must be doubled, for a pressurizing or braking function there are accordingly twice the number of pressure control valves 26 in addition to the 2/2-valves 24.

If sudden stopping (emergency braking) of the drive unit is to take place by turning off all directional control valves, or unintentionally high-external loads on the oil or fluid circuit otherwise occur, fundamentally the pressure in the lines, for example the supply lines 20, or in the valve housing, could increase such that failure of a component can occur. To counteract this, in the indicated circuit other pressure control valves 28 as so-called shock valves are installed and when a definable pressure is reached, enable circulation of the fluid or oil in its own circuit. The described functions need never be switched at the same time for reliable operation and the indicated valve means are present for optional all-wheel drive for each axle to be triggered according to the circuit diagram in FIG. 1.

In the altered embodiment as shown in FIG. 2 with the valve according to the invention, the same components as in FIG. 1 are also labeled with the same reference numbers. The plurality of illustrated individual valves according to the solution as shown in FIG. 1 is replaced in the circuit diagram as shown in FIG. 2 by a valve according to the invention which interacts with a shuttle valve 32 as another valve, the three fluid ports 1, 2, and 3 being indicated and the control means of the valve being labeled 4′. Furthermore, the valve has another, fourth fluid port which is connected to the tank 16 via the connecting line 34 and is used for unpressurized diversion of the pilot oil. The indicated valve arrangement with the shuttle valve 32 is switched between the two supply lines 20 via the connection sites 36. The proportional valve used in the circuit diagram of FIG. 2 is shown in particular in different embodiments as illustrated in FIGS. 3 to 5, in the embodiment as shown in FIG. 3 the shuttle valve 32 being shown again by a symbol. The latter is no longer shown in the illustrated longitudinal valve sections as shown in FIGS. 4 and 5, for the sake of simpler illustration.

Before the function of the hydraulic circuit as shown in FIG. 2 is detailed, first the proportional control valve as shown in FIGS. 3 to 5 will be detailed below.

The valve, especially the proportional pressure control valve, as shown in FIG. 3 has a valve housing 38 in the manner of a screw-in cartridge. On the free face end of the valve housing 38 there is one fluid port 1 and along the outer periphery of the valve housing 38 the other fluid ports 2, 3, and 4 penetrate the pertinent valve housing 38 in the radial direction. The individual fluid ports 1, 2; 3 and 4 are accordingly separated fluid-tight from one another by way of seals which are located on the outer peripheral side on the valve housing 38. Furthermore, as shown symbolically in FIG. 3, the shuttle valve 32 with its input sides is connected to the fluid ports 1, 2 and 3 and to the connection sites 36 which as shown in FIG. 2 discharge into the supply lines 20 (not shown in FIG. 3).

The valve housing 38, as shown, is made as a screw-in cartridge and can be screwed in this way into the connection unit of the drive unit which is not shown with its all-hydraulic system. On its end opposite the fluid port 1 the valve housing 38 is provided with a control means 40 which made in the manner of a magnet system has a magnet armature 42 which energized by means of a coil (not shown) can move back and forth within a pole tube 44 and in doing so for triggering a closing part 48 in the form of a closing cone acts on the actuating rod 46. The closing part 48 and actuating rod 46 are separated from one another via a compression spring 50 as an energy storage device. Both the closing part 48 and also the compression spring 50 as well as the front end of the actuating rod 46 facing away from the magnet armature 42 are guided in a fluid space 52 which can be connected to carry fluid via the fluid port 4 to the connecting line 34 as shown in FIG. 2, which discharges with its free end into the tank 16.

Within the valve housing 38 a valve piston 56 is guided, the valve piston 56 being made in the manner of a primary stage and the component 58 constituting the pilot seat of the valve in the manner of a pre-stage. The valve piston 56 with its one face end borders another fluid space 60 in which as another energy storage device a compression spring 62 is guided which engages a hollow-cylindrical recess in the valve piston 56. The valve piston 56 is furthermore provided on the outer peripheral side with a radial recess 64 which has an axial length, viewed in the lengthwise direction of the valve, which is dimensioned such that in definable switching or displacement positions of the valve piston 56 in any case a fluid-carrying path between the fluid ports 2 and 3 is partially cleared, and again, as is shown in FIG. 3, can be blocked. Both the valve piston 56 and also the pilot seat 58 have fluid channels 66, 68 which pass in the lengthwise direction and which viewed in the direction of looking at FIG. 3 on their right end have one orifice 70 each which choke the fluid flow which is present on the fluid port 1.

Flow through the proportional valve shown in FIG. 3 can take place in both directions, that is, from fluid port 2 to fluid port 3 or vice versa. The direction of the throughflow is among other things determined by where the highest consumer pressure prevails in the supply lines 20. This consumer pressure is reported by the shuttle valve 32 via a signaling line 72 to the fluid port 1 of the proportional valve. If the closing pressure which can be set by the magnet system of the control means 4′ is exceeded by the consumer pressure prevailing on the fluid connection 1 raising the closing part 48 off the pilot seat 58 as the pre-stage, the pilot control opens in this way and the valve piston 56 which is designed as the primary stage moves against the force of the energy storage device in the form of a compression spring 62 to the left. In this way the fluid-carrying connection is opened from fluid port 2 to fluid port 3 and fluid (oil) can flow from the higher to the lower pressure level. In the de-energized state, that is, when the magnet system has not been activated, the proportional valve meets the requirement for unpressurized oil circulation of one axle (axle free running), for which in the past an additional 2/2-way valve 22 (cf. FIG. 1) was necessary according to the prior art.

For partially energized setting of the magnet system and therefore partial activation of the magnet armature 42, with the valve solution according to the invention the function of the described pressurizing is implemented in which the hydraulic motor 10 can be braked by way of a defined pressure, and with the solution according to the invention the brake action can be proportionally set via the magnetic force of the magnet system. This valve function then replaces the existing combination of the pressure control valve 26 with the 2/2-way valve 24 as the overall pressurizing system (cf. FIG. 1). For complete energization and therefore the highest magnet closing force, the proportional valve according to the invention performs the function of the previously known shock valves 28 as independent pressure control valves. Another advantage of the solution according to the invention is that the reference of the proportional valve can be placed against the pressure in the tank 16 so that the pressures on the outflow side can no longer be added to the set pressure.

The altered embodiments as shown in FIGS. 4 and 5 will be explained in that they differ essentially from the valve solution as shown in FIG. 3. In terms of their actual valve structure, the three designs as shown in FIGS. 3 to 5 correspond to one another and the essential differences can be seen only in the scope of execution of the respective control means 4′.

In the embodiment as shown in FIG. 4, the magnet system as the control means 4′ was replaced by mechanical presetting with which via a spindle 74 and force spring 76 the closing pressure for the closing part 48 can be dictated by hand. The valve is made as a double-acting, pilot-controlled shock valve with tank reference via the connecting line 34, the double action being based on the decoupling of the control port 1 from the consumer ports 3 and 4. This valve version is both defined (black/white—switching behavior) and can also be proportionally triggered.

While the embodiment as shown in FIG. 3 has a so-called pushing magnet system in which in the energized state the magnet armature 42 seeks to keeps the closing part 48 in its closed position which blocks the channel 68 via the actuating rod 46, in the solution as shown in FIG. 5 the magnetic system with the magnet armature 42 is made as a so-called pulling system in which the magnet armature 42 under the influence of an energized winding coil (not shown) viewed in the direction of looking at FIG. 5 moves from right to left against the action of the force spring 76 as part of mechanical presetting according to the solution shown in FIG. 4. The embodiment as shown in FIG. 5 therefore combines a pulling magnetic system with mechanical presetting according to the solution as shown in FIG. 4. If the assignable pole tube 44 is made as a so-called fail-safe pole tube, this enables other versions. Thus, at full energization unpressurized circulation is enabled and in the de-energized state of the magnetic system as the switching means 4′ there would be a type of fail-safe valve with the function of a double-acting, pilot controlled shock valve with a tank reference. The maximum pressure can then be manually set, similarly to as in a normal pressure control valve. This de-energized state is shown in this way in FIG. 5.

If the proportional drive according to the invention is used in the described hydraulic vehicle drive, a clear reduction of the number of required valves is possible and altogether the installation space for the valve design is reduced. Since flow takes place through the proportional valve according to the invention in both directions, twice the number of valves according to the known solution as shown in FIG. 1 is eliminated. On the basis of the consideration that no two functions need proceed at the same time, in this way alternative switching of the proportional valve according to the hydraulic switching design as shown in FIG. 2 can be used and thus a plurality of valves can be saved, which helps to reduce production and maintenance costs overall. The proportional valve, however, need not be limited to the use of vehicle drives, but can also be used in other hydraulic circuits based on its stable switching behavior, especially wherever increased safety requirements are emphasized. 

1. Valve, especially a proportional pressure control valve, with a valve housing (38) with at least three fluid ports (1, 2, 3), the valve being connectable to a hydraulic drive system with a definable consumer pressure, characterized in that it is possible for a control means (40) to trigger a valve piston (56) which is dynamically connected to a pilot seat (58) by means of an energy storage device (62), and that the prevailing consumer pressure at one fluid port (1) acts at least on the valve piston (56) such that depending on the prevailing consumer pressure and on the actuating force of the control means (40) fluid can flow through between the two other fluid ports (2 and 3) in both directions within the valve housing (38).
 2. The valve according to claim 1, wherein between the two other fluid ports (2, 3) a shuttle valve (32) is connected and renders the highest consumer pressure on one fluid port (1) via a signaling line (72).
 3. The valve according to claim 1, wherein one fluid port (1) discharges on the front side into the free end of the valve housing (38) and wherein the other two fluid ports (2, 3) penetrate the valve housing (38) along its outer periphery and can be connected to one another to carry fluid by means of the valve piston (56) as the primary stage depending on its position.
 4. The valve according to claim 3, wherein the pilot seat (58) acts as a pre-stage and can be exposed to a definable actuating force by the control means (4′).
 5. The valve according to one of claim 1, wherein the energy storage device is made as a compression spring (62) between the valve piston (56) and the pilot seat (58).
 6. The valve according to claim 1, wherein the valve piston (56) and the pilot seat (58) are each penetrated by a connecting channel (66, 68) which is provided on its side facing the consumer pressure with an orifice (70) or choke.
 7. The valve according to claim 6, wherein the connecting channel (68) of the pilot seat (58) can be closed by a closing part (48) of the control means (4′).
 8. The valve according to claim 1, wherein the valve piston (56) and the pilot seat (58) are kept at a distance to one another by means of the energy storage device with the formation of a fluid space (60).
 9. The valve according to claim 1, wherein the control means (4′) has a magnet system with triggerable magnet armature (42) which acts on the valve piston (56) and the pilot seat (58), or consists of mechanical presetting (74) or of a combination of a magnetic system with mechanical presetting.
 10. The valve according to claim 1, wherein it has a further fourth fluid port (4) which is used for unpressurized diversion of the pilot oil. 